#include<stdio.h>
#include<iostream>
#include<string.h>
using namespace std;
int main()
{
	int n,sum = 0;
	cin >> n;
	if (n > 1)	for (int i = 1; i <= n; i++)sum += i;
	else for (int i = n; i <= 1; i++)sum += i;
	cout << sum << endl;
	return 0;
}